Heterostructure for electronic power components, optoelectronic or photovoltaic components

ABSTRACT

A heterostructure that includes, successively, a support substrate of a material having an electrical resistivity of less than 10 −3  ohm·cm and a thermal conductivity of greater than 100 W·m −1 ·K −1 , a bonding layer, a first seed layer of a monocrystalline material of composition Al x In y Ga (1-x-y) N, a second seed layer of a monocrystalline material of composition Al x In y Ga (1-x-y) N, and an active layer of a monocrystalline material of composition Al x In y Ga (1-x-y) N, and being present in a thickness of between 3 and 100 micrometers. The materials of the support substrate, the bonding layer and the first seed layer are refractory at a temperature of greater than 750° C., the active layer and second seed layer have a difference in lattice parameter of less than 0.005 Å, the active layer is crack-free, and the heterostructure has a specific contact resistance between the bonding layer and the first seed layer that is less than or equal to 0.1 ohm·cm 2 .

This application is a 371 filing of International Patent ApplicationPCT/EP2010/068614 filed Dec. 1, 2010 and a continuation of applicationSer. No. 12/956,675 filed Nov. 30, 2010.

FIELD OF THE INVENTION

The present invention relates to a heterostructure for the manufactureof electronic power components or optoelectronic components, orphotovoltaic components successively comprising from its base to itssurface:

-   -   a support substrate,    -   a bonding layer,    -   a crack-free monocrystalline layer, so-called “active layer,” of        a material of composition Al_(x)In_(y)Ga_((1-x-y))N, where        0≦x≦1, 0≦y≦1 and x+y≦1, presenting a thickness of between 3 and        100 micrometers, in which or on which the components are        manufactured.

BACKGROUND OF THE INVENTION

For the vertical or planar electronic power device (MOS components,bipolar transistors, J-FET, MISFET, Schottky or PIN diodes, thyristors),optoelectronic component (Laser, LED) and photovoltaic component (solarcells) market, it is interesting to utilize an Al_(x)In_(y)Ga_((1-x-y))N(x between or equal to 0 and 1, y between or equal to 0 and 1, x+y lessthan or equal to 1) conducting substrate and preferably a bulk GaN (or“freestanding”) substrate.

These substrates are, however, difficult to manufacture with currenttechnologies and remain very expensive.

A proposed alternative consists of a heterostructure comprising a thickactive layer of Al_(x)In_(y)Ga_((1-x-y))N (preferably in doped GaN)formed on a conductive substrate.

But the growth of thick layers with a good crystalline quality is stilldifficult with current methods if the seed substrate is not of the samematerial as the material epitaxied.

The epitaxy of a thick layer of GaN (approximately 10 micrometers) on aseed substrate such as doped Si or SiC, due to the differences in thecoefficient of thermal expansion (CTE) and lattice parameter between thematerials, leads to the formation of defects and cracks in the layerwhich reduces the effectiveness of the electronic, optical oroptoelectronic devices formed on this material.

In addition, as document WO 01/95380 discloses, this epitaxynecessitates the utilization of a buffer layer—for example a layer ofAlN—between the seed substrate and the GaN that presents high electricresistance.

The epitaxy of a thick layer of GaN on a sapphire substrate followed bythe transfer of the layer to a conductive substrate by laser detachmentis an expensive process.

In addition, the choice of these materials does not allow a dislocationdensity of less than 10⁷ cm⁻² to be reached in the active layer.

In addition, the layer thus formed presents very significant bendingwhich necessitates long preparation steps (polishing, etc.) so that itmay be bonded and transferred to a final substrate.

In addition, the transfer of a layer of GaN from a bulk substrate by theSMARTCUT® technology does not enable the desired thicknesses to bereached in a satisfactory manner to date.

Document US 2008/0169483 describes the formation of an epitaxy substratecomprising a seed layer of GaN transferred by the SMARTCUT® technologyto a support substrate.

A layer of conductive GaN is then deposited on the seed layer and thenit is transferred to a thermally and electrically conductive support.

This method is complex since it involves two transfers of the activelayer of GaN to form the final conductive structure.

Document US 2009/278233 describes the formation of a heterostructure forlight-emitting devices.

The manufacturing of the heterostructure comprises first a step ofproviding on a handle substrate a seed layer suited for the epitaxialgrowth of an active layer made of a III/N material and a step of growingthe active layer on the seed layer, thus producing an intermediatestructure.

This intermediate structure is then bonded to a final substrate,preferably via a eutectic bonding layer, and the handle substrate isremoved.

This method is thus complex since it involves the use of two differentsupport substrates, the first one for the epitaxial growth of the activelayer, the second one for the operation of the component.

Therefore one seeks to design a heterostructure for electronic powercomponents, optoelectronic components or photovoltaic components and amethod of manufacturing the heterostructure in view of obtaining athick, crack-free monocrystalline layer of a material of compositionAl_(x)In_(y)Ga_((1-x-y))N on a support substrate, not presenting thedisadvantages of methods from the prior art. In particular, asimplification of the process steps is sought.

More precisely, the heterostructure must present the followingproperties:

-   -   a thick active layer, i.e., with a thickness greater than or        equal to 3 micrometers, preferably greater than 10 micrometers,    -   a good vertical electrical conductivity despite interfaces        between different materials forming the heterostructure, i.e., a        total electrical resistivity of less than or equal to 10⁻²        ohm·cm,    -   a low electrical resistivity of the support substrate, i.e.,        typically lower than 10⁻³ ohm·cm,    -   a high thermal conductivity of the heterostructure, i.e.,        typically greater than or equal to 100 W/m·K,    -   a low dislocation density in the active layer, i.e., of less        than or equal to 10⁷ cm⁻².

In the case of electronic power components, the active layer of theheterostructure shall comprise a main portion with a thicknessrepresenting between 70 and 100% of the thickness of the active layer,the main portion being weakly doped so as to enable a dispersion of theelectric field over the thickness of the active layer.

In the present text, “layer portion” is understood to refer to a part ofa layer considered in the sense of the thickness of the layer. Thus, alayer may be constituted of several stacked portions, the sum of thethicknesses of portions being equal to the total thickness of the layer.The different portions of the active layer may be in the same material,but with different doping, or rather may be in different materials ofcomposition Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and x+y≦1.

Thus, the active layer of a PIN diode may be designed with alternatingInGaN/GaN/InGaN or doped p GaN/weakly doped GaN/doped n GaN layers.

The active layer for optoelectronic or photovoltaic components may beconstituted of a stack of layers in different materials of compositionAlxInyGa(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1.

In addition, “subjacent” designates a layer portion the farthest removedfrom the surface of the heterostructure and “superjacent” designates alayer portion closest to the surface of the heterostructure. By way ofexample, the active layer of a PIN diode comprises a single subjacentand superjacent layer on both sides of the main portion.

Another object of the invention is to design a support adapted forepitaxy of the active layer in view of forming the heterostructuredescribed above.

More precisely, this epitaxy support must enable growth of the thickactive layer without forming cracks and must in addition presentelectric properties compatible with the intended applications.

BRIEF DESCRIPTION OF THE INVENTION

For this purpose, a first object of the invention relates to aheterostructure for the manufacture of electronic power components,optoelectronic components or photovoltaic components comprisingsuccessively from its base to its surface:

-   -   a support substrate in a material presenting an electrical        resistivity of less than 10⁻³ ohm·cm and a thermal conductivity        of greater than 100 W·m⁻¹·K⁻¹,    -   a bonding layer,    -   a monocrystalline seed layer in a material of composition        Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and x+y≦1,    -   a monocrystalline layer, so-called “active layer”, of a material        of composition Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and        x+y≦1.

This heterostructure is remarkable in that:

-   -   the active layer is a crack-free monocrystalline layer        presenting a thickness of between 3 and 100 micrometers;    -   the specific contact resistance between the seed layer and the        bonding layer is less than or equal to 0.1 ohm·cm², and    -   the materials of the support substrate, the bonding layer and        the seed layer are refractory at a temperature of greater than        750° C., preferably at a temperature of greater than 1000° C.,        and    -   the seed layer presents a difference in the lattice parameter        with the material of the active layer of less than 0.005 Å.

As will be apparent in the detailed description to follow, the supportof the heterostructure, i.e., the support composed of the supportsubstrate, the bonding layer and the seed layer is, on the one hand,suited for the epitaxial growth of the active layer and, on the otherhand, presents the required properties for the operation of thecomponents that are made or on in the active layer.

In other words, the support that is used to grow the active layer isdesigned so as to have thermal and electrical properties that render italso suitable for the subsequent operation of the components, withoutany need to be replaced by another support in view the operation of thecomponents.

In the present text, “refractory material” is understood to refer to amaterial that does not deteriorate at the epitaxy temperature of thelayer of material of composition AlxInyGa_((1-x-y))N (whether by meltingor chemical reaction with gas components), and in which the electricaland thermal conductivity characteristics are not altered at thistemperature (particularly by deterioration of the interfaces with othersupport layers).

It is specified that, in the whole of the present text, the coefficientof thermal expansion is considered to be the linear coefficient ofthermal expansion along a plane parallel to the surface of the layers atthe epitaxy temperature of the active layer with relation to the bondingtemperature. The vapor phase epitaxy temperature of the active layer oftype AlGaInN is conventionally less than 1100° C. Bonding is generallycarried out at ambient temperature.

The coefficient of thermal expansion is conventionally measured by X-raydiffraction or by dilatometry.

Electrical conductivity (or electrical resistivity) and specific contactresistance are measured by standardized methods that are well known tothe person skilled in the art and detailed, for example, in the booktitled “Semiconductor Material and Device Characterization” by DieterSchöder (John Wiley & Sons). Specific contact resistance is measured,for example, by TLM (“Transmission Line Method” or “Transfer LengthMethod”). This method consists of depositing metal contacts with alength l and a width w, spaced apart by a distance Li over the layer ofsemiconductor material with a thickness h. Resistance Ri is measuredbetween different contacts so as to measure several resistance valuesfor different distances Li between the contacts. These values aretransferred to an orthogonal mark whose axes represent the resistancesRi and the distances Li. The slope and the zero distance point of thestraight line obtained by joining the points enables the resistivity ofthe semiconductor material and the specific contact resistance to berespectively extracted.

Thermal conductivity is measured by standardized methods well known tothe person skilled in the art and are detailed, for example, in thetreatise R-2-850 “Conductivité et diffusivité thermique des solides”[Conductivity and thermal diffusivity of solids] by Alain Degiovanni,published by Techniques de I'lngénieur.

Dislocation density may be measured by transmission electron microscopyor by cathodoluminescence.

According to other characteristics of the heterostructure, consideredalone or in combination:

-   -   the active layer presents a dislocation density of less than 10⁸        cm⁻², and preferably less than 10⁷ cm⁻²;    -   the seed layer is doped with a concentration of dopants of        between 10¹⁷ and 10²⁰ cm⁻³;    -   the dopants are preferably n-type dopants;    -   the material of the support substrate is a metal chosen from        among tungsten, molybdenum, niobium and/or tantalum and their        binary, ternary or quaternary alloys, such as TaW, MoW, MoTa,        MoNb, WNb or TaNb;    -   advantageously, the support substrate is in TaW comprising at        least 45% tungsten or in MoTa comprising more than 65%        molybdenum;    -   the material of the bonding layer comprises polycrystalline        silicon, silicide, preferably tungsten silicide or molybdenum        silicide, tungsten, molybdenum, zinc oxide, a metal boride such        as zirconium boride, tungsten boride, titanium boride or        chromium boride, and/or indium tin oxide;    -   the bonding layer is preferentially in a material presenting an        electrical resistivity of less than or equal to 10⁻⁴ ohm·cm;    -   the seed layer presents an electrical resistivity of between        10⁻³ and 0.1 ohm·cm.

When the heterostructure is intended for the manufacture of electronicpower components, the active layer presents a main portion in which thethickness represents between 70 and 100% of the thickness of the activelayer and in which the concentration of dopants is less than or equal to10¹⁷ cm⁻³, and the coefficient of thermal expansion of the supportsubstrate material is between a minimum coefficient of less than0.5·10⁻⁶ K⁻¹ to that of the coefficient of thermal expansion of thematerial of the main portion of the active layer and a maximumcoefficient of greater than 0.6·10⁻⁶ K⁻¹ to the coefficient of thermalexpansion of the material of the main portion of the active layer at theformation temperature by epitaxy of the active layer.

According to a particular embodiment of the heterostructure, the mainportion of the active layer is inserted between a subjacent layer and asuperjacent layer, each comprising a concentration of different typedopants greater than 10¹⁷ cm⁻³. The material of the main portion and ofthe subjacent and superjacent portions is then preferably GaN.

According to another embodiment of the heterostructure, the main portionof the active layer is inserted between a subjacent portion and asuperjacent portion, each of these portions being constituted of amaterial Al_(x)In_(y)Ga_((1-x-y))N of a different composition.

According to another embodiment of the heterostructure, the thickness ofthe main portion represents 100% of the thickness of the active layerand the material of the main portion is n-type doped GaN, preferablysilicon doped GaN.

Preferably, the main portion of the active layer and the seed layer areconstituted of the same material.

In an example of embodiment of the heterostructure, the supportsubstrate is in molybdenum, the bonding layer is in tungsten, the seedlayer is in GaN and the active layer is in GaN.

Another object of the invention is an electronic power, optoelectronicor photovoltaic component formed in or on the active layer of theheterostructure described above, and comprising at least one electricalcontact on the active layer and one electrical contact on the supportsubstrate.

Another object of the invention relates to a method of manufacturing aheterostructure for the manufacture of electronic power components,optoelectronic components or photovoltaic components, characterized inthat it comprises:

-   -   (a) the provision of a support substrate presenting an        electrical resistivity of less than 10⁻³ ohm·cm and a thermal        conductivity of greater than 100 W·m⁻¹·K⁻¹,    -   (b) the provision of a donor substrate, the substrate comprising        a monocrystalline seed layer adapted for the epitaxial growth of        the layer,    -   (c) the formation of a bonding layer on the donor substrate        and/or on the support substrate,    -   the materials of the support substrate, the seed layer and the        bonding layer are chosen to be refractory at a temperature        greater than 750° C., preferably at a temperature greater than        1000° C., and chosen such that the specific contact resistance        between the seed layer and the bonding layer is less than or        equal to 0.1 ohm·cm²,    -   (d) bonding by molecular adhesion of the donor substrate on the        support substrate, the bonding layer being situated at the        interface,    -   (e) thinning of the donor substrate to transfer it from the seed        layer to the support substrate,    -   (f) growth by epitaxy of a monocrystalline layer, so-called        “active layer,” of a material of composition        Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and x+y≦1, on the        seed layer, without cracking, until a thickness of between 3 and        100 micrometers is obtained,        wherein the material of the seed layer is chosen to present a        lattice parameter difference with the material of the main        portion of the active layer of less than 0.005 Å.

According to other characteristics of the method, considered alone or incombination:

-   -   the active layer presents a main portion whose thickness        represents between 70 and 100% of the thickness of the active        layer (4) and whose concentration of dopants is less than or        equal to 10¹⁷ cm⁻³ and the material of the support substrate is        chosen such that its coefficient of thermal expansion is between        a minimum coefficient of less than 0.5×10⁻⁶ K⁻¹ to the        coefficient of thermal expansion of the material of the main        portion of the active layer and a maximum coefficient of greater        than 0.6×10⁻⁶ K⁻¹ to the coefficient of thermal expansion of the        material of the main portion of the active layer at the epitaxy        temperature of the active layer;    -   the method advantageously comprises doping of the active layer,        the doping being carried out for epitaxy step (f) or, after        epitaxy, by implantation or diffusion of dopant species;    -   preferably, the material of the support substrate is a metal        chosen from among tungsten, molybdenum, niobium and/or tantalum        and their binary, ternary or quaternary alloys, such as TaW,        MoW, MoTa, MoNb, WNb or TaNb;    -   the seed layer is formed in the donor substrate by ionic        implantation so as to create in the donor substrate an        embrittlement zone at a depth substantially equal to the        thickness of the seed layer;    -   the implantation step is carried out after the formation of the        bonding layer on the donor substrate, the implantation being        carried out through the bonding layer;    -   the method comprises doping of the seed layer, the doping being        carried out by implantation or diffusion of dopant species;    -   when the roughness of the donor substrate or support substrate        is less than 1 nm for a 5 micrometer×5 micrometer surface        measured by AFM and presents a peak valley surface topology of        less than 10 nm, the bonding layer is only deposited on the        other substrate;    -   when the roughness of the support substrate is greater than or        equal to 1 nm for a 5 micrometer×5 micrometer surface measured        by AFM and presents a peak valley surface topology greater than        or equal to 10 nm, the bonding layer is deposited and polished        until a roughness of less than 1 nm and a peak valley surface        topology of less than 10 nm is reached.

BRIEF DESCRIPTION OF THE FIGURES

Other objects, characteristics, and advantages of the invention willemerge from the following detailed description, with reference to theattached drawings in which:

FIG. 1 illustrates a heterostructure in conformance with the invention,

FIG. 2 schematically illustrates the formation of the seed layer in thedonor substrate,

FIG. 3 illustrates the formation of a bonding layer on the supportsubstrate,

FIG. 4 illustrates the assembly of the donor substrate on the supportsubstrate before the fracture,

FIG. 5 illustrates the structure resulting from the fracture of thedonor substrate,

FIG. 6 illustrates another example of a heterostructure in conformancewith the invention,

FIG. 7 illustrates an example of an electronic power component formed ona heterostructure in conformance with the invention.

It is specified that, for reasons of figure readability, the scales ofthickness of the different layers have not been respected.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a heterostructure 1 proposed in the presentinvention comprises an active layer 4 of a material of compositionAl_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and x+y≦1.

Layer 4 is called active since it is the layer in or on which theelectronic power components such as MOS, J-FET, MISFET, Schottky diodesor even thyristors; or LED components, lasers, solar cells are intendedto be formed.

The thickness of the active layer 4 is between 3 and 100 micrometers,preferably between 3 and 20 micrometers, further preferably on the orderof 10 micrometers.

The active layer 4 is bonded onto a support substrate 10 through abonding layer 2 whose properties will be detailed below.

The active layer 4 is formed by epitaxy on a seed layer 3 that, as willbe seen later, may be in the same material as that of the active layer 4or in a different material.

The manufacturing method of such a heterostructure 1, which will bedescribed in detail later, mainly comprises the following steps:

-   -   the provision of the support substrate 10;    -   the provision of a donor substrate comprising a seed layer 3        adapted for the epitaxy of the active layer 4;    -   the transfer of the seed layer 3 to the support substrate 10,        the bonding layer 2 mentioned above being formed at the        interface;    -   the growth by epitaxy of the active layer 4 on the seed layer 3.

The assembly of the support substrate 10, the bonding layer 2 and theseed layer 3, which constitutes a support for the epitaxy of the activelayer 4 allowing the heterostructure illustrated in FIG. 1 to be formed,presents a total electrical resistivity of less than or equal to that ofthe bulk GaN comprising a dopant concentration of 10¹⁸ cm⁻³, i.e., atotal electrical resistivity of less than or equal to 10⁻² ohm·cm andpreferentially a thermal conductivity on the order of magnitude as thatof the GaN, i.e., greater than or equal to 100 W/m·K so as to propose analternative to the utilization of a bulk GaN substrate, that isdifficult to find on the market and is expensive.

Thus, heterostructure 1 such as defined above presents a sufficientvertical electrical conductivity for the intended applications such asthe operation of Schottky diodes.

In addition, the materials constituting heterostructure 1 and themanufacturing methods are chosen such that the heterostructure mayresist epitaxy temperatures of the active layer without deterioratingthe materials or their electrical and thermal properties and thus enableoperation of devices equivalent to devices formed from a bulk III/Nmaterial.

Support Substrate

A support substrate 10 is in a material presenting an electricalresistivity of less than 10⁻³ ohm·cm and a thermal conductivity ofgreater than 100 W·m⁻¹·K⁻¹.

The material of the support substrate 10 is also “refractory,” i.e., itpresents thermal stability at active layer formation temperatures.

It presents a coefficient of thermal expansion close to that of thematerial of active layer 4 at epitaxy temperature to prevent stressingof the epitaxied layer during the heating preceding growth and duringcooling of the heterostructure after epitaxy.

For example, the epitaxy temperature in vapor phase by MOCVD, HVPE ofthe GaN and the AlN to date is around 1000° C.-1100° C., and around 800°C. for InGaN and Al_(x)In_(y)Ga_((1-x-y))N.

In fact, if the coefficient of thermal expansion of the supportsubstrate 10 is less than (respectively, greater than) that of the seedlayer 3, the seed layer 3 will be in compression (respectively, intension) at the epitaxy temperature.

Such being the case, this constraint in tension or in compression may beharmful to the quality of the epitaxy.

In addition, if the epitaxied layer 4 is relaxed during the epitaxy andits coefficient of thermal expansion is greater than (respectively, lessthan) that of the support substrate 10, it will be in tension(respectively, in compression) during cooling.

Beyond a threshold thickness, the constraints in tension as incompression are likely to relax by the formation of cracks orcrystalline defects in the epitaxied layer, which reduces the efficacyof the devices formed from this layer.

The sufficiently “close” character of the coefficient of thermalexpansion of the support substrate with relation to that of the activelayer is determined as a function of the predominant material chosen forthe active layer, i.e., the material of the main portion whereappropriate.

Thus, for example, for an active layer 4 in GaN (whose coefficient ofthermal expansion is on the order of 5.6·10⁻⁶ K⁻¹), the supportsubstrate 10 may present a coefficient of thermal expansion of between5.1·10⁻⁶ and 6.1·10⁻⁶ K⁻¹ at the epitaxy temperature of the activelayer.

In general, it is considered that the coefficients of thermal expansionof the active layer (noted CTE_(active layer)) and of the supportsubstrate (noted CTE_(support)) must be linked by the followingrelationship:CTE_(active layer)−0.5·10⁻⁶K⁻¹≦CTE_(support)≦CTE_(active layer)+0.6·10⁻⁶ K⁻¹

The support substrate 10 is metal-based and is preferably chosen fromamong tungsten (W), molybdenum (Mo), niobium (Nb) and/or tantalum (Ta)and their binary, ternary or quaternary alloys, such as TaW, MoW, MoTa,MoNb, WNb or TaNb.

In particular, the TaW alloy comprising at least 45% tungsten(preferably 75%) is likely to present a coefficient of thermal expansionin accordance with that of GaN while possessing good thermal andelectrical conductivity properties.

The MoTa alloy comprising more than 65% molybdenum is also suitable.

The characteristics of some materials are found in the table below, forindicative purposes.

CTE at ambient CTE at Thermal Electrical temperature 1000° C.conductivity resistivity (10⁻⁶ K⁻¹) (10⁻⁶ K⁻¹) (W/mK) (microohm · cm) Mometal 4.8 5.6-6.0 140 5 W metal 4.5 5.1 165 5 Ta metal 6.3 7.0 54 13 Nbmetal 7.3 8.3 54 15 GaN 3.5 5.6 150

The support substrate 10 is obtained, for example, by sintering (for theW for example) or by hot pressing.

Depending on the nature of the material of the support substrate 10 andthe epitaxy temperature of the active layer 4 (for a material of theAlInGaN type, this varies between 800° C. and 1100° C.), evaporation ordiffusion of the support substrate may be produced, with the effect ofcontaminating the active layer.

In this case, one may encapsulate the support substrate 10 by aprotective layer (not represented) in view of the application of thermalbudgets of active layer growth. For example, a layer of silicon nitrideor aluminum nitride may be deposited on the rear face and the lateralfaces of the support substrate by a CVD or PVD deposition (respectively“Chemical Vapor Deposition” and “Phase Vapor Deposition”).

Seed Layer

The monocrystalline seed layer 3 is in an Al_(x)In_(y)Ga_((1-x-y))Nmaterial, where 0≦x≦1, 0≦y≦1 and x+y≦1 and is electrically conductive.The layer is obtained by transfer to the support substrate 10 from adonor substrate 30, which may be bulk or rather formed of several layers(for example, a layer of GaN deposited on a sapphire support).

The material of the seed layer 3 is refractory, i.e., it does notdeteriorate during epitaxy of the active layer.

The seed layer 3 transfer method is obtained by a step of bonding thedonor substrate 30 by molecular adhesion on the support substrate 10followed by a step of thinning the donor substrate 30 to obtain the seedlayer 3. This thinning may be carried out by any technique adapted tothe materials utilized and whose implementation is well known to theperson skilled in the art, such as chemical mechanical polishing CMP,grinding, laser irradiation at the interface between two layersconstituting the donor substrate or preferably a SMARTCUT®-type method.A detailed description of this method may, for example, be found inEuropean Patent EP0533551 or in the book “Procédé SMARTCUT dansSilicon-On-Insulator Technology: Materials to VLSI (SMARTCUT Method inSilicon-on-Insulator Technology), 2nd Edition by Jean-Pierre Colingefrom Kluwer Academic Publishers, p. 50 and 51.

Schematically, with reference to FIG. 2, the seed layer 3 is defined inthe donor substrate 30 by carrying out an implantation of ionic species(for example, hydrogen) in which the implantation peak of the specieshas a depth substantially equal to the desired thickness for the seedlayer 3. The zone with the maximum implanted species concentrationconstitutes an embrittlement zone 31 that may be fractured by theapplication, for example, of an adapted thermal budget.

The thickness of the seed layer is preferentially between 100 nm and 500nm.

The material chosen for the seed layer 3 preferably presents a latticeparameter adapted to the epitaxial growth of the active layer 4.

Preferably a material presenting a difference in lattice parameter withthe material of the active layer 4 of less than 0.005 Å is chosen.

For example, one may thus carry out an epitaxy of InGaN at 1.4% In on aseed layer of GaN, or rather an epitaxy of AlGaN at 6.5% Al on a seedlayer of GaN.

According to another example, for epitaxy of an active layer of GaN of athickness of between 3 and 100 micrometers, one may remove a seed layerfrom a bulk substrate of GaN.

Preferably, the seed layer 3 is removed from the N polarity face of thedonor substrate 30 such that the layer bonded to the support substrate10 presents an exposed face of Ga polarity, from which the resumption ofepitaxy is easier with current techniques.

Nevertheless, one may also remove the seed layer from the Ga polarityface of the donor substrate so as to carry out epitaxy on the N polarityface of the seed layer or carry out a double transfer so as to obtain anexposed face of the seed layer of Ga polarity.

Ideally, the material of the seed layer 3 is the same as that of theepitaxied active layer 4 (this is then homoepitaxy).

It then presents the same crystalline structure and, provided that thesupport substrate does not lead to constraints in the seed layer, thereis no lattice parameter difference between the material of the seedlayer and that of the active layer, which prevents the formation of newdefects in the epitaxied crystal.

Homoepitaxy (active layer of GaN epitaxied on a seed layer of GaN) thusenables the lowest possible dislocation density to be obtained in theactive layer.

In the case of homoepitaxy, the seed layer may be distinguished from theactive layer by a difference in resistivity of these two layers when theactive layer and the seed layer present different doping. In the absenceof doping, it is sometimes possible to distinguish the interface betweenthe two layers by TEM (Transmission Electron Microscopy).

In addition, the seed layer 3 advantageously presents an electricalresistivity of between 10⁻³ and 0.1 ohm·cm.

This resistivity is preferably the lowest possible resistivity,approximately 10⁻³ ohm·cm, in order to facilitate making ohmic contactwith the support substrate, which corresponds to a concentration ofdopants of between 10¹⁷ and 10²⁰ cm⁻³.

The material of the seed layer 3 and its level of doping are chosen soas to prevent constituting an electrical conduction barrier between theactive layer 4 and the support substrate 10 of the finalheterostructure.

The desired dopant may already be present in the layer removed from thedonor or doping may be carried out by diffusion or implantation ofdopant species before epitaxy of the active layer 4, depending on thedesired device. Preferably, this n-type doping (for example by silicon)is easier to carry out, especially as it facilitates making electricalcontact with the bonding layer 2.

In addition, the seed layer 3 is sufficiently thin (between 100 nm and500 nm, for example) so that the effect of its coefficient of thermalexpansion is negligible compared to that of the support substrate 10 andthat of the active layer 4.

Active Layer

To respond to the conductivity criterion of heterostructure 1 and to beable to support a large electric field (i.e., on the order of 10⁶V·cm⁻¹), when the heterostructure 1 is intended for electronic powercomponents, the epitaxied active layer 4 of Al_(x)In_(y)Ga_((1-x-y))Ncomprises dopants with a concentration of less than or equal to 10¹⁷cm⁻³, in order to disperse as much as possible the electric potentialdrop over the entire thickness of the layer.

Doping is obtained, for example by incorporating silicon, which leads ton-type doping.

Doping may be carried out during growth of the active layer 4.

Thanks to the choice of the material of the seed layer 3, thedislocation density in the active layer is less than 10⁸ cm⁻²,preferably less than 10⁷ cm⁻².

In addition, a wise choice of the support substrate 10, such as statedabove, enables a thick active layer 4, free from cracks, to be obtainedover a thickness of between 3 and 100 micrometers, preferablyapproximately 10 micrometers.

By way of information, it is specified that the term “crack” in thepresent invention is differentiated from dislocation in that the crackin a film of crystalline material corresponds to a crystalline cleavagethat extends more or less deeply in the thickness of the film, i.e., aseparation of the material into two parts, which creates, on both sidesof the cleavage, two free surfaces in contact with air, while the filmcomprising a dislocation remains continuous.

According to a preferred embodiment, active layer 4 is made of GaN.

According to a particular embodiment illustrated in FIG. 6, active layer4 is composed of a plurality of portions of layers, that is, by goingfrom the bonding layer to the free surface of the active layer: aportion 4 a of doped n-type GaN, a main portion 4 b, whose thickness isgreater than or equal to 70% of the total thickness of the active layer,of weakly doped GaN (i.e., with a concentration of less than or equal to10′17 cm⁻³) and a portion 4 c of doped p-type GaN, or conversely.

According to another example, the active layer 4 of a PIN diode isconstituted of a main portion 4 b of GaN, a subjacent portion 4 a ofInGaN and a superjacent portion 4 c of InGaN.

As is well known to the person skilled in the art, these dopings enablethe desired electrical contacts to be obtained, for example in view ofproducing a PIN diode.

Preferably, doping of the active layer 4 is carried out during epitaxy,with a precursor gas such as silane for n-type doping to silicon, or aprecursor such as CP₂Mg for p-type doping to magnesium.

Alternately, doping may be obtained by implantation (for example siliconfor n-type doping, or magnesium for p-type doping) or yet, for thesuperjacent portion, by diffusion of species in the portion (for examplesilicon for n-type doping, magnesium for p-type doping).

Bonding Layer

A bonding layer is made in one or more materials chosen such that thebonding energy between the support substrate and the implanted donorsubstrate is greater than the fracture thermal budget.

Competition between the fracture at the embrittlement zone 31 and theseparation of substrates 10, 30 at the bonding interface, which leads toa partial, poor-quality fracture of the embrittlement zone, is thusavoided.

In particular, the bonding layer is in a refractory material that doesnot deteriorate at the epitaxy temperature of the active layer.

In addition, the material of bonding layer 2 and its thickness arechosen so as to minimize the electric potential drop at the bonding.

Generally, the thickness of bonding layer 2 is thus less than or equalto 1 micrometer.

This thickness may be greater depending on the roughness of thesubstrate on which it is formed that it is necessary to smooth foreffective bonding; In this case, the electric potential drop will beminimized by the choice of a material presenting a lower electricalresistivity.

Preferably, bonding layer 2 is electrically and thermally conductive,and the material composing the layer preferably presents an electricalresistivity of less than or equal to 10⁻⁴ ohm·cm.

However, considering that its thickness is much less than that of thesupport substrate, the influence of electrical and thermalconductivities of the material constituting the layer remains limited.

It is therefore possible to choose for this layer other materials thanmetals.

The bonding layer 2 in addition enables low electrical contactresistance between one of its faces and the active layer on the onehand, and between its other face and the support substrate on the otherhand.

It is particularly desirable that the specific contact resistancebetween bonding layer 2 and seed layer 3 is less than or equal to 0.1ohm-cm² in order to maintain good vertical electrical conductivitydespite an interface presenting a semiconductor material.

To do this, the materials from bonding layer 2 and seed layer 3 arechosen such that their output energy, i.e., minimum energy, measured inelectron-volts, necessary to detach an electron from the Fermi level ofa material until a point situated at infinity outside the material, isin the same order of magnitude.

A material pair satisfying this requirement is for example GaN/W, theoutput energy of the n-type doped GaN being approximately 4.1 eV whilethat of the W is approximately 4.55 eV. Another pair considered may beGaN/ZrB2 (the output energy of ZrB2 is approximately 3.94 eV).

A layer of titanium may also promote adhesion and making contact betweenthe material of the seed layer in III/N material and the bonding layer,since it participates in lowering the height of the conduction barrierat the interface (the output energy of Ti is approximately 4.33 eV).

A layer of titanium with a thickness of 10 nm deposited on the materialof seed layer 3 or the material of bonding layer 2 before assembly issufficient to obtain the anticipated effect.

Thermal annealing of the two materials also enables the specific contactresistance to be improved by better interconnection of the materials atthe interface.

The bonding layer is deposited on donor substrate 30 before implantationand/or on support substrate 10. The act of carrying out implantation inthe donor substrate after deposition of the bonding layer prevents therisk of a fracture at the implanted zone due to the thermal budgetproduced by the deposition.

When layers of bonding material are deposited on both the donorsubstrate and the support substrate, bonding layer 2 is constituted ofthe whole of these two layers.

It is noted that when the roughness of one of the substrates (i.e., ofthe donor substrate or of the support substrate) is less than 1 nm for a5 micrometer×5 micrometer surface measured by atomic force microscopy(AFM) and when it presents a peak valley surface topology of less than10 nm measured by optical profilometry with a Wyko-type apparatus, thebonding layer only has to be deposited on the other substrate. It isobserved that the measured roughness is generally similar for a surfaceranging from 1 micrometer×1 micrometer to 10 micrometers×10 micrometers.

Polycrystalline silicon (p-Si) is a material of choice that adheres wellto the GaN, which enables planarization of the surface of the metallicsupport substrate and which is easy to polish.

A surface roughness before bonding of, at the most, a few angstroms rmsmay thus be reached.

To minimize the possible diffusion of silicon to the epitaxied layer 4,a diffusion barrier (not represented) may be provided, for examplebetween the seed layer and the bonding layer. For example, thisdiffusion barrier may be a film of AlN of a few nanometers of thickness.

In the case of diffusion of silicon in vapor phase during epitaxy fromthe lateral walls of the layer to the outside of the structure, a layerforming a diffusion barrier of the lateral zones not covered by the p-Silayer may be provided.

Alternately, one may also form the bonding layer 2 by depositing a metal(for example tungsten or molybdenum), a metal oxide such as zinc oxide,a silicide formed ex-situ (for example SiW₂ or SiMo) or a metal boride(such as TiB₂, chromium boride, zirconium boride or tungsten boride) onthe donor substrate 30 before implantation and/or on the supportsubstrate 10.

In a variation, it is possible to deposit a metal on the donor substrate30 or the support substrate 10 and to deposit a silicide or a boride onthe other substrate; the bonding layer 2 will then be constituted of thecombination of this metal with the silicide or the boride.

Another possibility consists of making the bonding layer 2 in indium tinoxide (ITO).

As the indium tin oxide is thermally unstable, it is preferablyencapsulated before carrying out epitaxy of the active layer 4.

The table below gives the properties of some of the materials that aresuitable for bonding layer 2.

The characteristic indicated in line Li is the melting point (expressedin ° C.); the characteristic of line L2 is the thermal conductivity (inW·m⁻¹·K⁻¹); that of line L3 is the electrical resistivity (in ohm·cm)and that of line L4 is the coefficient of thermal expansion (in 10⁻⁶K⁻¹).

p-Si MoSi₂ TaSi₂ WSi₂ NbSi₂ L1 1412 1870 2499 2320 2160 L2 130 58.9 L31.0 · 10⁻⁴ 2.2 · 10⁻⁵ 8.5 · 10⁻⁶ 3.0 · 10⁻⁵ 5.0 · 10⁻⁵ L4 8.12 8.8-9.54ZrB₂ WBx TiB₂ CrB₂ L1 3060 2385 2980 1850-2100 L2  58  64 20-32 L3 9.2 ·10⁻⁶ 4.0 · 10⁻⁶ 1.6-2.8 · 10⁻⁵ 2.1 · 10⁻⁵ L4

Example of Embodiment No. 1 Bonding Layer in p-Si

First the donor substrate 30 is prepared by the following steps (seeFIG. 2):

-   -   Preparation of the N polarity face of a bulk substrate 30 of        GaN. This step involves known planarization and polishing        techniques.    -   CVD or PVD deposition on the face of layer 21 of p-Si with a        thickness of 100 to 500 nm.    -   Implantation in the donor substrate 30 of ionic species (of        hydrogen, for example) through layer 21 of p-Si. The depth of        implantation determines the thickness of the seed layer 3 of        GaN. For indicative purposes, the implantation energy is between        80 and 180 keV and the dose is between 2 and 4·10¹⁷ at/cm².    -   Polishing by CMP (Chemical Mechanical Polishing) of layer 21 to        reach a roughness compatible with bonding. Typically, the        roughness before bonding must be on the order of a few angstroms        rms.

Second, with reference to FIG. 3, the support substrate 10 is prepared,which is in a TaW alloy containing 75% tungsten.

This preparation comprises the deposition on support substrate 10 of alayer 22 of p-Si with a thickness of a few hundred nanometers.

The thickness of layer 22 is adapted as a function of the morphology ofthe surface of the support substrate 10, such that the planarization byCMP of the layer of p-Si enables a surface roughness of a few angstromsrms to be reached.

Then a chemical treatment prior to adhesion of the two layers 21, 22 ofp-Si is carried out by hydrophilic or hydrophobic bonding.

For this purpose, the surfaces are cleaned to remove contaminants and anoxidizing or deoxidizing treatment is possibly performed on the surfacesby plasma activation, drying and exposure to atmospheres containingozone (for oxidation). The surfaces to be bonded may also be preheatedup to a temperature of approximately 200° C.

With reference to FIG. 4, the surfaces of the two layers 21, 22 of p-Siare placed in contact; therefore a bonding layer 2 of p-Si with a totalthickness of 100 nm to 1 micrometer is formed.

Optionally, bonding is consolidated by a thermal treatment applied fromambient temperature to approximately 200° C. with a duration of a fewminutes to 2 hours.

Then the fracture thermal budget is applied with a temperature ramp ofbetween ambient temperature and approximately 600° C.

The structure illustrated in FIG. 5 is then obtained.

The damaged material on the fractured surface is removed (i.e., thesurface of seed layer 3) to reach a roughness of a few angstroms to afew nanometers rms, adapted for a resumption of epitaxy.

The heterostructure 1 illustrated in FIG. 1 is obtained by growing theactive layer 4 on seed layer 3, on the desired thickness.

The residue of the donor substrate 30 may also be recycled by removing,by ion beam etching or chemical etching, the p-Si on the non-fracturedface.

Example of Embodiment No. 2 Bonding Layer in WSi₂

First the donor substrate is prepared, which includes the followingsteps (see FIG. 2):

-   -   Planarization and polishing of the N polarity face of a bulk        substrate 30 of GaN.    -   Deposition on the face of layer 21 of WSi₂ silicide with a        thickness of 100 to 500 nm.    -   Implementation of annealing to form ohmic contact with the GaN.        This annealing is carried out at a temperature of between        600° C. and 1200° C. for a few minutes under neutral atmosphere        comprising NH₃ and has the effect of reducing the contact        resistance.    -   Implantation of ionic species, such as hydrogen, through layer        21 of WSi₂ in the donor substrate 30 to a depth determining the        thickness of the seed layer 3 of GaN. The implantation energy is        typically between 80 and 180 keV.    -   Polishing by CMP of the WSi₂ to reach a roughness compatible        with bonding (i.e., a few angstroms rms).

Second, preparing the support substrate 10 in TaW comprising 75%tungsten. For this purpose (see FIG. 3), a layer 22 of WSi₂ with athickness of a few hundred nanometers is deposited on substrate 10.

As stated above, the thickness of the layer 22 of WSi₂ is adapted as afunction of the morphology of the surface of the support substrate 10such that the planarization by CMP of the layer 22 of WSi₂ enables asurface roughness of a few angstroms rms to be reached.

If necessary, annealing to form ohmic contact with the TaW is carriedout. The conditions of this annealing are a temperature of between 600°C. and 1200° C., a duration of a few minutes and a neutral atmosphere.

Planarization by CMP of the surface of the WSi₂ is then carried out.

Then a chemical treatment prior to adhesion of the two layers of WSi₂ iscarried out by hydrophilic or hydrophobic bonding.

For this purpose, the surfaces are cleaned to remove contaminants and anoxidizing or deoxidizing treatment is possibly performed on the surfacesby plasma activation, drying and exposure to atmospheres containingozone (for oxidation). The surfaces to be bonded may also be preheatedup to a temperature of approximately 200° C.

The surfaces of the two layers 21, 22 of WSi₂ are then placed incontact; therefore a bonding layer 2 of WSi₂ with a total thickness of100 nm to 1 micrometer is formed.

Optionally, bonding is consolidated by a thermal treatment applied fromambient temperature to approximately 200° C. with a duration of a fewminutes to 2 hours.

Then the fracture thermal budget is applied with a temperature ramp ofbetween ambient temperature and approximately 600° C.

The damaged material on the fractured surface is removed (i.e., thesurface of seed layer) by dry etching (RIE) or chemical mechanicalpolishing (CMP) to reach a roughness of a few angstroms to a fewnanometers rms, adapted for a resumption of epitaxy.

The heterostructure 1 illustrated in FIG. 1 is obtained by growing theactive layer 4 on seed layer 3, on the desired thickness.

The residue of the donor substrate may also be recycled by removing, bydry etching (for example by reactive ionic etching RIE) or wet etching(i.e., chemical etching), the WSi₂ on the non-fractured face.

Example of Embodiment No. 3

First the donor substrate 30 is prepared by the following steps (seeFIG. 2):

-   -   Preparation of the N polarity face of a bulk substrate 30 of        GaN. This step involves known planarization and polishing        techniques.    -   CVD or PVD deposition on the face of layer 21 of W with a        thickness of 100 to 500 nm.    -   Implantation in the donor substrate 30 of ionic species (of        hydrogen, for example) through layer 21 of W. The depth of        implantation determines the thickness of the seed layer 3 of        GaN. For indicative purposes, the implantation energy is between        80 and 180 keV and the dose is between 2 and 4·10¹⁷ at/cm².    -   Polishing by CMP (Chemical Mechanical Polishing) of layer 21 to        reach a roughness compatible with bonding.

Typically, the roughness before bonding must be on the order of someangstroms rms.

Second, with reference to FIG. 3, the support substrate 10 is prepared,which is of molybdenum.

This preparation comprises the deposition on support substrate 10 of alayer 22 of W with a thickness of a few hundred nanometers.

The thickness of layer 22 is adapted as a function of the morphology ofthe surface of the support substrate 10, such that the planarization byCMP of the layer of W enables a surface roughness of a few angstroms rmsto be reached.

Then the two surfaces of layers 21 and 22 of W are placed in contact forbonding by molecular adhesion, thus a bonding layer 2 of W with a totalthickness of 100 nm to 1 micrometer is formed.

Optionally, bonding is consolidated by a thermal treatment applied fromambient temperature to approximately 200° C. with a duration of a fewminutes to 2 hours.

Then the fracture thermal budget is applied with a temperature ramp ofbetween ambient temperature and approximately 600° C.

The structure illustrated in FIG. 5 is then obtained.

The damaged material on the fractured surface is removed (i.e., thesurface of seed layer 3) to reach a roughness of a few angstroms to afew nanometers rms, adapted for a resumption of epitaxy.

The heterostructure 1 illustrated in FIG. 1 is obtained by growing theactive layer 4 of GaN on seed layer 3, on the desired thickness.

Components Based on the Heterostructure

The heterostructure 1 described above can then be used to formelectronic power components, optoelectronic components or photovoltaiccomponents in or on the active layer 4.

In particular, the components that can be based on the heterostructurecomprise electronic power components such as MOS components, bipolartransistors, J-FET, MISFET, Schottky or PIN diodes, thyristors;optoelectronic components (e.g., Laser, LED) and photovoltaic components(solar cells).

To that end, at least one electrical contact may be formed on the activelayer 4 of the heterostructure (which represents the “front side” of thecomponent), and at least one electrical contact may be formed on thesupport substrate 10 of the heterostructure (which represents the “backside” of the component).

In the case of optoelectronic components, the active layer may berelatively thin, i.e., up to 6 micrometers.

In the case of photovoltaic or optoelectronic components, the contactformed on the active layer may be transparent or semitransparent inorder to allow the transmission of the appropriate wavelength.

The skilled person is able to define an appropriate material for thecontact so as to meet this requirement.

Example of an Electronic Power Component

FIG. 7 illustrates a vertical transistor with a vertical gate (alsocalled a “trench gate MOSFET”) made from heterostructure 1 obtainedthanks to the present invention.

On the rear face of support substrate 10, a metallic layer 100 (forexample, of aluminum) may be deposited to form a drain ohmic contact.However, the conductivity of the support substrate of the invention ischosen so as to not inevitably necessitate such a contact layer.

The active layer 4 of the heterostructure successively comprises asubjacent portion 4 a of doped n− GaN, a main portion of doped p+GaNwith magnesium, and two superjacent regions 4 c of doped n+GaN forsource contacts with layers 200 that are, for example, in analuminum/titanium alloy.

The two regions 4 c are deposited on both sides of a trench to form thevertical gate.

The gate trench is covered with a layer 300 of a dielectric substance(such as SiO₂ or SiN) and the trench is filled with polycrystallinesilicon 400.

Of course, the embodiments that have just been described in detail areonly examples of implementation of the present invention, but in no wayconstitute limitations.

In particular, the invention may be implemented with other choices ofmaterials, according to the criteria stated above.

What is claimed is:
 1. A heterostructure for the manufacture of electronic power components, optoelectronic components or photovoltaic components, comprising: a support substrate comprising a material presenting an electrical resistivity below 10⁻³ ohm·cm and a thermal conductivity that is above 100 W·m⁻¹·K⁻¹, a bonding layer upon the support substrate, a first layer upon the bonding layer, the first layer comprising a monocrystalline material of composition Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and x+y≦1, a second layer upon the first layer, the second layer comprising a monocrystalline material of composition Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and x+y≦1, and an active layer upon the second layer, the active layer comprising a monocrystalline material of composition Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and x+y≦1 and being present in a thickness of between 3 and 100 micrometers, wherein the materials of the support substrate, the bonding layer and the first layer are refractory at a temperature of above 750° C., the active layer and second layer have a difference in lattice parameter of below 0.005 Å, the active layer is crack-free, and the heterostructure has a specific contact resistance between the bonding layer and the first layer that is equal to or below 0.1 ohm·cm², and wherein the active layer presents a main portion having a thickness representing between 70% and 100% of that of the active layer and which thickness of the main portion has dopants at a concentration that is equal to or below 10¹⁷ cm⁻³, and wherein the support substrate material has a coefficient of thermal expansion of between a minimum coefficient and a maximum coefficient, wherein the minimum coefficient is no more than 0.5×10⁻⁶ K⁻¹ lower than that of the coefficient of thermal expansion of the material of the main portion of the active layer and the maximum coefficient is more than 0.6×10⁻⁶ K⁻¹ above the coefficient of thermal expansion of the material of the main portion of the active layer at temperatures where the active layer is formed by epitaxy.
 2. The heterostructure according to claim 1, wherein the active layer presents a dislocation density that is lower than 10⁸ cm⁻² and the main portion of the active layer is located between subjacent and superjacent layers of the active layer, each of the subjacent and superjacent layers comprising dopants of a different type at a concentration of more than 10¹⁷ cm⁻³.
 3. The heterostructure according to claim 2, wherein the material of one of the main, subjacent and superjacent portions is GaN that is optionally doped with silicon.
 4. The heterostructure according to claim 2, each of the main, subjacent and superjacent portions is constituted of a material Al_(x)In_(y)Ga_((1-x-y))N with each portion having a different x or y composition.
 5. The heterostructure according to claim 2, wherein the material of the main portion is of silicon doped n-type GaN.
 6. The heterostructure according to claim 2, wherein the main portion of the active layer and the first seed layer are constituted of the same material.
 7. The heterostructure according to claim 1, wherein the material of the support substrate is a metal chosen from the group consisting of tungsten, molybdenum, niobium, tantalum and their binary, ternary or quaternary alloys, including TaW, MoW, MoTa, MoNb, WNb or TaNb.
 8. The heterostructure according to claim 7, wherein the support substrate is TaW comprising at least 45% tungsten or MoTa comprising more than 65% molybdenum.
 9. The heterostructure according to claim 1, wherein the material of the bonding layer comprises polycrystalline silicon, tungsten or molybdenum silicide, tungsten, molybdenum, zinc oxide, a metal boride or indium tin oxide and the first layer is doped with a concentration of between 10¹⁷ and 10²⁰ cm⁻³ of n-type dopants.
 10. The heterostructure according to claim 1, wherein the bonding layer comprises a material presenting an electrical resistivity that is lower than or equal to 10⁻⁴ ohm·cm, and the first layer has an electrical resistivity of between 10⁻³ and 0.1 ohm·cm.
 11. The heterostructure according to claim 1, wherein the support substrate comprises molybdenum, the bonding layer comprises tungsten, the first layer comprises GaN and the active layer comprises GaN.
 12. An electronic power, optoelectronic or photovoltaic component formed in or on the active layer of a heterostructure according to claim 1, comprising at least one electrical contact on the active layer and at least one electrical contact on the support substrate.
 13. A method of manufacturing the heterostructure of claim 1 for the manufacture of electronic power components, optoelectronic components or photovoltaic components, with the heterostructure comprising an active layer of a monocrystalline material of composition Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1, 0≦y≦1 and x+y≦1, which method comprises: providing a support substrate presenting an electrical resistivity below 10⁻³ ohm·cm and a thermal conductivity that is above 100 W·m⁻¹·K⁻¹, providing a donor substrate comprising the first and second layers of monocrystalline material adapted for epitaxial growth of the active layer, providing a bonding layer on one of the donor substrate or the support substrate, choosing the materials of the support substrate, the first and second layers and the bonding layer to be refractory at a temperature of above 750° C., such that the heterostructure has a specific contact resistance between the bonding layer and the first layer that is equal to or below 0.1 ohm·cm², choosing the support substrate material to have a coefficient of thermal expansion of between a minimum coefficient and a maximum coefficient, wherein the minimum coefficient is no more than 0.5×10⁻⁶ K⁻¹ lower than that of the coefficient of thermal expansion of the material of the main portion of the active layer and the maximum coefficient is more than 0.6×10⁻⁶ K⁻¹ above the coefficient of thermal expansion of the material of the main portion of the active layer at temperatures where the active layer is to be formed by epitaxy, choosing the material of the second layer to present a lattice parameter difference with the material of the active layer that is below 0.005 Å, bonding together by molecular adhesion the donor and support substrates with the bonding layer situated at the interface therebetween, thinning the donor substrate to expose the second layer upon the support substrate, and growing by epitaxy the active layer on the second layer to a thickness of between 3 and 100 micrometers without causing cracking of the active layer to form the heterostructure.
 14. The method according to claim 13, which further comprises doping the active layer during or after epitaxial growth by implantation or diffusion of dopant species, doping the seed layer by implantation or diffusion of dopant species, or doping both layers.
 15. The method according to claim 13, wherein the material of the support substrate is a metal chosen from the group consisting of tungsten, molybdenum, niobium, tantalum and their binary, ternary or quaternary alloys, including TaW, MoW, MoTa, MoNb, WNb or TaNb.
 16. The method according to claim 13, which further comprises forming the first layer in the donor substrate by ionic implantation so as to create in the donor substrate an embrittlement zone at a depth that is substantially equal to the thickness of the first layer.
 17. The method according to claim 16, wherein the ionic implantation is carried out after providing the bonding layer on the donor substrate, with the implantation being carried out through the bonding layer.
 18. The method according to claim 13, which further comprises providing a surface roughness on one of the donor substrate or support substrate that is less than 1 nm for a 5 micrometer×5 micrometer surface measured by AFM and presents a peak valley surface topology below 10 nm, with the bonding layer provided on the substrate that does not have the recited surface roughness.
 19. The method according to claim 13, which further comprises when the support substrate has a roughness that is greater than or equal to 1 nm for a 5 micrometer×5 micrometer surface measured by AFM and that presents a peak valley surface topology of at least 10 nm, the bonding layer is deposited on the support substrate and is polished until a roughness below 1 nm and a peak valley surface topology below 10 nm is reached. 